Plyometrics

Plyometric exercises  help to develop explosive strength and speed in fast twitch muscle fibers. These exercises use the inherant stretch-recoil properties of muscle (i.e., eccentric tension generated when the muscles are lengthened) to enhance subsequent shortening or concentric contractions. This is the dynamic action behind the rapid prestretch or "cocking" phase to "activate" these natural recoil properties.

Examples of this phase include taking the arm back into position prior to throwing a baseball or bending the knees prior to jumping. Thus athletes that rely on explosive strength and speed, such as sprinters and basketball players, include plyometrics in their training programs.

A plyometric movement can be broken down into three phases:
--Lengthening phase (eccentric contraction)
--Amortization phase
--Take-off (concentric contraction)

During the lengthening phase, the muscle creates tension like a spring being stretched. This type of contraction, called an eccentric contraction, occurs when performing movements such as jumping down from an object, running downhill, or lowering a weight. During the eccentric contraction, tension is built into the muscle as it lengthens. The take-off occurs via concentric contraction of the muscles. During this phase, the muscle shortens as it contracts, and actual work (i.e., movement of the body through space) is performed.

The amortization phase is the period of time from the beginning of the lengthening phase to the beginning of the take-off phase. This is the most important phase when it comes to plyometric training. During this phase, the muscle must convert the muscular tension generated during the lengthening phase to acceleration in a selected direction during the take-off phase.

The elastic properties inherent within the muscles and neuromuscular reflexes (the stretch reflex) are responsible for this conversion. Plyometric training may increase the efficiency of this conversion. The goal of plyometric training is to decrease the amount of time in the amortization phase and thereby increase speed.

While box jumping, if you step up and down, instead of jump up and down, these mechanisms and responses are blunted. This is why we perform box jumps, not box steps, and why you are asked to jump instead of step.

CFSF